P2B Mothership
While not an official 'X-plane,' the Douglas D558 series of aircraft certainly broke new barriers of flight. The D558-2 Skyrocket was the first manned aircraft to exceed twice the speed of sound. It was carried aloft by a converted Navy P2B bomber (the Navy version of the Air Force's B-29) in order to conserve its fuel for high speed and high altitude flight. David Newman sent along these photos from the NASA/Dryden photo archives.
